(1) Field of the Invention
The present invention relates to an image forming apparatus which forms an image by thermally fixing a developed image transferred on a recording medium.
(2) Background Art
An image forming apparatus, for example, like a laser printer, which forms an image by conveying a recording medium such as paper, transferring a developed image on the recording medium, and thermally fixing the developed image, has been conventionally known. Generally, the image forming apparatus comprises a heating body such as a heat roller for contacting a recording medium in a highly heated condition to thermally fix a developed image transferred on the recording medium, and a temperature sensor for detecting the temperature of the heat body. Based on the temperature detected by the temperature sensor, the image forming apparatus controls the temperature of the heat body suitable for thermal fixing.
In such an image forming apparatus, temperature control of the heating body can not be correctly performed, for example, if a heat source for heating the heating body is broken down and consequently the heating body is not adequately heated, and if the temperature sensor does not correctly detect the temperature of the heating body due to change in positional relationship between the heating body and the temperature sensor.
There is provided an image forming apparatus in which the image forming operation is not performed when the temperature of the heating body is determined as abnormal based on the temperature detected by the temperature sensor. However, it is not preferable that the image forming operation is not performed immediately after the temperature sensor temporarily mis-detects the temperature due to noise. Therefore, the number of times, in which the temperature of the heating body is determined as abnormal, is counted. Until the number of times reaches a predetermined number, the image forming operation can be resumed. When the number of times reaches a predetermined number, the image forming operation can not be performed (for example, see Publication of Unexamined Japanese Patent Application 8-292679).